If you inadvertently removed the Show Desktop tab from your Quick Launch bar and want to get it back, open Notepad and copy\paste the following text:

[Shell]Command=2IconFile=explorer.exe,3[Taskbar]Command=ToggleDesktop

Save the new file as Show Desktop.scf then drag and drop the icon on the Quick Launch bar.If you are generally a lazy person, then MS MVP Kelly Theriot has a fix which will restore the Show Desktop icon. This should work for all Windows versions.